Group proposes solution to plutonium puzzle

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Though the US and Russia are working on strategies for what to do with the 100 tons of plutonium being "retired" from warheads, both countries are focusing on options that cannot be implemented for decades. What can we do in the near term to safeguard these stockpiles from terrorists, especially in Russia?

A group of MIT researchers has a suggestion: bank it.

They are exploring an intermediate storage form for plutonium that would be relatively quick to implement and would keep it safe while the nations decide on--and establish the infrastructure for--more permanent solutions.

In this storage form, plutonium would be melted into massive glass logs. Unlike a similar strategy favored by others, the MIT logs would not include the high-level radioactive wastes that essentially immobilize the element for good. As a result, the "clean" MIT logs would be difficult to steal but would not preclude future uses for the element--an option important to Russia, which considers its plutonium a national resource and a future energy source.

"You can think of this intermediate storage form as a plutonium `bank,'" said Kory Budlong Sylvester, a graduate student in the Department of Nuclear Engineering. "It may not provide an acceptable level of security in the long-term, but it will provide a material barrier to direct theft, buying time to assess all long-term alternatives." Last month Mr. Sylvester presented a paper on this approach at the Fifth International Conference on Radioactive Waste Management and Environmental Restoration in Berlin.

Mr. Sylvester is part of the MIT Plutonium Group. This small group of researchers is "trying to identify the best way to immobilize plutonium, especially in the short term," said Kevin W. Wenzel, an assistant professor in the Department of Nuclear Engineering and leader of the group. "We're proposing that this intermediate storage form could be used to prevent proliferation of plutonium over the next five to 10 years while permanent techniques [for its disposal] are being decided on."

The two principal options for plutonium disposal that the superpowers are considering could take decades to implement for both technical and political reasons, the MIT researchers say. One option, favored by the US and similar to the MIT suggestion, involves melting the plutonium into a glass, a process known as vitrification. The other option, favored by Russia, would burn the plutonium as fuel in nuclear reactors.

The key difference between the long-term vitrification option and the shorter-term MIT suggestion is that the US proposes mixing the plutonium with the high-level radioactive wastes that are actually byproducts from its production. (Plutonium itself is not highly radioactive.) The resulting glass logs would be highly radioactive and very heavy, clear deterrents to thieves.

These barriers (particularly the radioactive barrier) also hamper plutonium extraction for peaceful purposes. As a result the Russians have balked at this option, said Mr. Sylvester, because it would preclude extracting the plutonium for use as a fuel.

The option favored by Russia, burning plutonium as a fuel in nuclear reactors, also makes the element more difficult for terrorists to get at. A small amount of the element is actually destroyed in the process, while that which remains is a mix of isotopes, or flavors, that makes it harder to use in weapons.

This "reactor-grade" plutonium is not as dangerous as the weapons-grade brand, but it is still a security threat. "You can still make a powerful explosive using reactor-grade plutonium," Mr. Sylvester said. For that reason the US disagrees with the Russian approach, and has banned the process here to set an example for other nations.

In contrast, Russia is keen on saving its plutonium as an energy source. At present, however, the country does not have the facilities to burn plutonium, so it is not an economical fuel. As a result, tons of the material could be stockpiled for years.

"I would sleep better at night if I knew there weren't thousands of intact plutonium pits [the grapefruit-sized spheres of plutonium removed from nuclear weapons in their dismantling] sitting around in Russia, given the political and economic instability in that country," Mr. Sylvester said.

Enter the MIT strategy. The researchers suggest vitrifying the plutonium, but doing so in a way that would not prevent later extraction for use as fuel. One could do so, they say, by vitrifying the element without the high-level radioactive wastes currently included in the recipe. As a result, the researchers hope that this alternative might be acceptable to Russia.

They note, however, that the plutonium in such a glass would not meet proposed US security standards. As a result, the National Academy of Sciences does not recommend intermediate storage forms. Essentially our government fears that the glass would not be nasty enough to dissuade terrorists.

"The question becomes, is it enough of a deterrent?" Mr. Sylvester said. He noted that the sheer size of the logs, which could be fashioned to weigh more than a ton, would still provide a hefty physical deterrent, since a person couldn't easily carry one away.

In addition, the Plutonium Group is using computer modeling to identify other elements that could be added to the recipe "to gum things up" and make it more difficult to extract the plutonium. Gary Cerefice, another graduate student in nuclear engineering and member of the group, "is playing terrorist," said Mr. Sylvester. "He's tearing apart my glass to determine how hard it is to get the plutonium out." [The glass being tested at MIT is made with thorium, a surrogate for plutonium, not the real thing.]

"The debate is really focused on what the final form of plutonium should be in 20 to 40 years," Mr. Sylvester concluded. "In my mind, our highest risk is today. We must act."

Other members of the MIT Plutonium Group, all affiliated with the Department of Nuclear Engineering, are graduate students Paul Chodak and Michael V. McMahon; Professors Michael J. Driscoll, Neil E. Todreas and Mujid S. Kazimi, head of the department, and senior research scientist Marvin M. Miller.

Professor Wenzel and Mr. Sylvester note that Dr. Scott Simonson, who is now at Knolls Atomic Power Laboratory in Schenectady, NY, began the MIT Plutonium Group three years ago when he was an assistant professor here. The work is funded in part by fellowships from the Department of Energy and the W. Alton Jones Foundation.

A version of this article appeared in MIT Tech Talk on October 25, 1995.